The present invention relates to a heat transfer image-receiving sheet improved in both printing properties (imagewise properties) and the storability of recorded images and, more particularly, to a heat transfer image-receiving sheet capable of making image representations excelling in color density, clearness and fastness properties, especially, light resistance, storability, etc.
Among various heat transfer techniques so far known in the art, there is a sublimation type of transfer system wherein a sublimable dye as a recording material is carried on a substrate sheet such as paper or a plastic film to make a heat transfer sheet, which is in turn overlaid on a heat transfer sheet dyeable with a sublimable dye, for instance, a heat transfer sheet comprising paper or a plastic film having a dye-receiving layer on its surface to make various full-color images thereon. In this system, the thermal head of a printer is used as heating means to transfer three-, four- or more-color dots by a very quick heating, thereby reconstructing a full-color image of an original manuscript by the multi-color dots.
Because the coloring material used is a dye, the thus formed image is so clear and so excellent in transparency that the resulting image representation can be improved in the reproducibility of halftone and-gray scale. This makes it possible to form image representations similar to those achieved with conventional offset or gravure printing and comparable in quality to full-color photographic images.
For the effective implementation of the heat transfer technique, the construction of an image-receiving sheet is as important as the construction of a heat transfer sheet.
To put it another way, the dye-receiving layer of the image-receiving sheet is required to excel in dye receptivity and take hold of a dye in place, after it has been transferred.
Improving the fixation of the dye transferred may be achieved by forming a dye-receiving layer of a resin having an increased dyeability. A problem with such a dye having an increased dyeability, however, is that the resulting image becomes blurred in the dye-receiving layer containing it during storage or degrades in storability. The fact that such a resin is inferior in dye-fixing properties leads to another problem that the dye is likely to bleed through the dye-receiving layer, contaminating other articles in contact with its surface. Still another problem is that such a resin causes the associated heat transfer sheet to adhere to the image-receiving sheet during heat transfer, peeling off the dye layer.
These problems may be solved by forming a dye-receiving layer of a resin making the received dye difficult to migrate through the dye-receiving layer. A problem with such a resin, however, is that it is so inferior in dye-fixing properties that image of high density and clearness can not be obtained.
In order to solve the above-mentioned two major problems, the use of a mixture of a resin having an increased dyeability with a resin having a reduced dye migration may be envisaged. This, however, offers no effective solution, since that mixture is intermediate in nature between both the resins.